Fluorescent device and method of making the same



Patented July 5, 1949 2,455,529 FLUORESCENT DEVICE AND METHdD OF MAKINGTHE SAME Joseph L.

swim-r, Cleveland Heights, and Robert C. Swltzer, South Euclid, Ohio NoDrawing. Original application October 9,

1941, Serial No. 414,285. plication April 12, 1M9, Serial No.

2 Claims. (Cl. 250-71) This invention relates to a luminescentcomposition, and, more particularly, to a thermo-set fluorescentresinous composition and a thermosetting fluorescent resinous fluid.This application is a division of our copending application Serial No.414,285, filed October 9, 1941, which, in turn, is acontinuation-in-part of our application, Serial No. 228,802, filedSeptember 7, 1938, now abandoned. fFluorescence," as that phenomenon isconsidered in this specification and claims, includes the phenomenon ofphosphorescence.

As pointed out in the above-identified application, heretoforefluorescent compositions, particularly fluorescent coatings, have tendedto deteriorate over short periods of time if the compositions wereexposed to sunlight or other light containing actinic radiations,hereinafter simply termed light." Therefore, fluorescent compositionshave been generally unsatisfactory heretofore upon prolonged exposure tolight, and it is a primary object of this invention to provide afluorescent composition and also a coating composition which willwithstand prolonged exposure to light as well as most commerciallyacceptable non-fluorescent coating compositions, such as paints,lacquers, and the like, which will withstand such exposure. While theinability of the fluorescent compositions known to the prior art towithstand prolonged light exposure is not fully understood, we havefound by our discoveries. which will be set forth below, that loss influorescence upon exposure to light is not a purely inherent andinescapable characteristic of fluorescent compositions, as was taught byapparently reliable prior art. In other words, at the time we commencedour research for a material which would maintain a substantially stablefluorescent brightness under light exposure, it was generally acceptedthat prolonged exposure to light exhausted brilliantly fluorescentsubstances of their fluorescent properties and the problem was to find anew fluorescent substance or substances which would retain brilliantfluorescence after a prolonged exposure to light. Through a series ofcomparative life tests in which samples of known fluorescent materialswere exposed to actinic radiations only and other sampleswere exposed toboth actinic radiations and the atmosphere, we have discovered that theloss in fluorescence of fluorescent substances and fluorescentcompositions containing a fluorescent ingredient is due to either theactual chemical decomposition of the fluorescent substances in thepresence of moisture vapor or Divided and this ap- 2 like reactivevapors and gases and/or the reaction of the fluorescent ingredient withits vehicle. We also discovered that actinic radiations, such as thosefound in sunlight, accelerate the decomposition and/or reaction of thefluorescent substances but were apparently not solely responsible forthe deterioration of the fluorescent substances.

Having discovered the foregoing facts, the problem of obtaining acomposition having stable fluorescent brilliance became one of finding asuitable vehicle which would be inert with respect to the fluorescentingredients and substantially completely impervious to moisture vaporand like reactive gases. A further requirement of a suitable vehicle wasthat it should be transparent to the visible light emitted by thefluorescent in-' gredients and which would not yellow and, therefore,lose its transparency upon exposure to weathering conditions. Further,in the majority of applications, the fluorescent ingredients wereingredients which were required to fluoresce under invisiblefluorescigenous radiations. Therefore, the vehicle should also betransparent to invisible fluorescigenous radiations. As a result of theforegoing discoveries and known facts, we assumed that a transparentnonyellowing vehicle which was non-reactive with the fluorescentingredients and which would substantially completely envelope thefluorescent ingredients would produce a fluorescent coating compositionwhich would retain the fluorescent brightness of the ingredients uponexposure to light. This assumption was apparently confirmed by carefullycompounded paints comprising a flu.- orescent pigment, anon-reactiveair-drying solvent, and a chemically indifferent transparent resin, suchas a methacrylate or polystyrene resin, for example, but such paintswould only maintain the fluorescent brightness of the pigments until thevehicle tended to break down under weathering conditions,

In endeavoring to flnd a vehicle for fluorescent pigments more stablethan the air-drying type,

we experimented with thermo-setting resins.

Known thermo-setting transparent and non-yellowing coating vehiclescomprised three general classes, phenolic resins, alkyd resins, andplasticized alcohol modified urea-formaldehyde resins. The advantages ofsuch thermo-setting resins were that, after thermo-setting, they formedhard. dense compositions characterized by their insolubility andinfusibility. Furthermore, such thermo-set' resins generally adhered orfused firmly to non-absorptive surfaces, such as metal or glass.

It is an object of this invention to provide a fluorescent compositionand resinous coating fluid possessing the advantages of thermo-settingvehicles, but, in general, thermo-setting vehicles are very reactivewith respect to suitable fluorescent pigments and, as expected, the heatemployed to thermo-set the vehicles rapidly accelerates the reactionbetween the vehicle and the fluorescent pigments.

The foregoing discoveries seemed to ban the use of substantially anentire class of brilliantly fluorescent ingredients, namely, fluorescentdyes. Obviously, the only manner in which dyes could be enveloped in avehicle was to dissolve the dye in the vehicle or to obtain a suspensionwhich would substantially amount to a solution. With a few exceptions,fluorescent dyes were not soluble in suitable non-yellowingair-dryingresins, such as the methacrylate or polystyrene types. Further,substantially all fluorescent dyes are notably unstable as compared withfluorescent pigments. When fluorescent dyes were dissolved or suspendedin known non-yellowing thermosetting resins, the dyes deterioratedrapidly during the process of thermo-setting the resins.

We have, however, discovered that an excellent non-reactivethermo-setting resinous vehicle for fluorescent pigments and dyesconsists of an alcohol-modified urea-formaldehyde resin containing noplasticizer. For example, such resin may be butyl alcohol-modifiedurea-formaldehyde. alcohol-modified urea-formaldehyde resin is verydense and glass-hard, transparent to both visible and ultra-violetlight, and non-yellowing. A film of such resin, however, is very brittleand nonadherent to non-absorptive surfaces, such as metal, although itwill form a very strong bond to glass. As a result of the brittleness of a film of alcohol-modified urea-formaldehyde resin, this resin wasnever used heretofore in-a coating composition vehicle except incombination with plasticizers, usually alkyds. Why fluorescent pigmentsand dyes do not react with alcohol-modifled urea-formaldehyde resins inthe absence of plasticizers, particularly during the application of heatto thermo-set the resin, is not understood. Neither is it understood whyfluorescent dyes are soluble in this one type of resin and are notgenerally soluble in other non-reactive resins. However, we have foundthat substantially all known fluorescent dyes are soluble to a certainextent, at least, in non-plasticized alcohol-modified ureaformaldehyderesins and, when dissolved in the thermo-set resin, the fluorescentbrightness of the dye is stabilized under exposure to light andatmospheric conditions.

Another transparent thermo-setting resin which will dissolve manyfluorescent dyes is ureaformaldehyde resin. Such resin, when thermoset,is extremely hard, dense, brittle, and incompatible with plasticizers.This resin has never been used as a coating composition vehicle, sinceit has no appreciable adhesion or film strength and will shattersubstantially spontaneously when thermo-set as a film or sheet.

The thermo-set fluorescent dyed resinous compositions made according toour invention are hard, dense, impervious to reactive gases, and willmaintain brilliant fluorescence after prolonged exposure to light undercomparatively severe weathering conditions. We have also found that Suchgreater than that usually employed in thermosetting resinous coatingcompositions.

Our manner of employing the dyed coating composition made accordingtoour invention may be in one of the following general methods, namely, bypartly or completely impregnating a fibrous sheet with the fluorescentdyed resinous liquid, air-drying the solvent, and then thermosetting theresin; or by dissolving a fluorescent dye in the resin, thermo-settingthe dyed resin, grinding the resinous composition into a fine pigment,and then dispersing the pigment into any suitable vehicle.

As specific examples of our invention, the following are set forth forpurposes of illustration and not by way of limitation:

Example 1. Aplurality of fibrous sheets, such as cloth or paper, areimpregnated, as by dipping. with a butyl alcohol solution ofalcohol-modified -urea-formaldehyde resin, or other suitablethermo-setting resins, and then air-dried. The sheets are preferablywhite or the resin may contain a dispersion of white or other lightreflecting nonfluorescent pigment. Another fibrous sheet is thenimpregnated with a butyl alcohol solution of alcohol-modifiedurea-formaldehyde resin, having proper viscosity for dipping, andcontaining not more than 5% nor less than 0.2% by weight of the solidresin of a fluorescent dye, such as meta diethylaminophenol-phthalein,dissolved in the resin. After the sheet impregnated with the fluorescentresin is air-dried, it is placed at the top or bottom of a stack ofsheets impregnated with the non-fluorescent material in a suitableheated press. With the press heated from 150 F. to 300 F., the stack ofimpregnated sheets is subjected to pressure ranging between 3500 to 1500pounds per square inch to fuse the thermo-setting resin into a dense,impervious mass enclosing the fibrous sheets. The time the sheets arekept in the press depends, of course, upon the with the fluorescent dyedresin placed in a press under 2500 pounds per square inch pressure andmaintained at 250 F. for one-half hour, a dense,

' hard sheet, having a plurality of lamina of fibrous material and afluorescent surface, will be formed. The surface of the sheet willretain its fluorescent brightness under prolonged exposure to light.Obviously, both the top and bottom sheets, or all the sheets stacked inthe press, may be impregnated with the dyed resin, but since it isusually desired to have only the surface of the fused sheet fluorescent,it is usually suflicient to have only one, or two, outer laminaimpregnated with the fluorescent resin.

the solid resin of fluorescent dye, such as p,p' di [p" (p"aminobenzolylamino) benzoylamino] stilbene o,o' di (sodium sulphonate).The airdried sheet is then stacked with other sheets impregnated with asuitable thermo-setting resin.

The stacked sheets are placed in a heated press and fused into a singlelaminated sheet in the manner described in Example 1.

Example 3.--A strong paper, such as 140 pound photogelatine printingstockmay be coated, by

6 dyed urea-formaldehyde and alcohol-modified urea-formaldehyde resinsmay be also employed in handling these same resins, termed genericallyurea-formaldehyde condensation products, havmeans of roll coatingequipment, for example,

with a 50% butyl alcohol solution of an alcoholmddifiedurea-formaldehyde resin containing in solution not more than nor lessthan 0.2%

by weight of the solid resin of a fluorescent xanthene basic dyestuif,such of meta ethylaminophenol-phthalein. This fluorescent coatingcomposition is preferably applied in a plurality of thin coats with ashort drying period allowed between coats so that the flrst coats willpartially impregnate the surface of the paper stock and the subsequentcoats will build up upon the first coats. vIt is then baked in a kiln attemperatures ranging from 150 to 300 F., the time the sheet remains inthe kiln dependas the ethyl ester in upon the temperatures employed, tofuse the thermo-setting resin into a dense, impervious film partlyimpregnated in the surface of the paper. Thus, a glassy, hard,luminescent film, resistant to light exposure under atmosphericconditions, will be formed on the surface of the paper if the air-driedcoating is baked at 200 F. for two hours or 250 F. for one hour.

Example 4.--For use in air-dryin coatings or in thermo-setting orthermoplastic coatings requiring great flexibility, our fluorescent dyedresinous composition may be employed as follows. A suitable fluorescentdye, such as meta ethylaniinophenol-phthalein is mixed with a freshaqueous suspension of urea-formaldehyde resin where the dye enters intosolution with theresin. Upon aging, the resin will coagulate and thesuspending medium is then decanted. The 00- agulated mass is then bakedto form a hard, brittle thermo-set resinous composition. Due to thebrittle infusible nature of the thermo-set resin, it may be ground intoa fine, nearly impalpable powder which is then dispersed into anysuitable transparent non-yellowing vehicle, such as a solution of anacrylic or polystyrene resin.

Example 5.Another manner of employing our resinous composition as apigment for an airdrying vehicle is to dissolve a desired quantity of afluorescent dye, such as the ethyl ester of metadiethylaminophenol-phthalein, in a butyl alcohol solution ofalcohol-modified urea-formaldehyde resin. Into the solution of alcohol,dye, and resin is mixed a suflicient quantity of low-test gasoline tocoagulate the resin. After decanting the liquid, the resinous mass isthen baked, ground, and dispersed in a suitable vehicle in the mannerdescribed in Example 4.

By the foregoing examples, we have shown our invention as a compositionof matter wholly or partly impregnated in a reinforcing material, and asa pigment for use in suitable vehicles. 0bviously, this invention is notlimited to its use in conjunction with the disclosed materials to whichthe luminescent composition is applied or which are incorporatedtherein. Furthermore, while the peculiar property of urea-formaldehyderesin and alcohol-modified urea-formaldehyde resin containing noplasticizers to dissolve and stabilize fluorescent dyes has beenparticularly useful in opening up new fields of use for fluorescentdyes, it should not be apparent that these same pure resins are alsonon-reactive with fluorescent pigments and will serve to envelope andstabilize them. Thus, our methods of handling tion are set 'ingincorporated therein fluorescent pigments such as the well knownfluorescent zinc sulphide and cadmium sulphide pigments.

pointed outin our prior applications, our fluorescent composition orcoating may be decorated or formedin many ways for use as signs.posters, displays, and the like. A particularly important application ofthis invention has been found in its use as name-plates or instrumentdials and panels which are printed or decorated with non-fluorescentsubstances. As illustrations, by way of example, and not by way oflimitation, the following examples of printing upon asurface comprisedof our fluorescent composiforth:

Example A.--A sheet having a surface of our fluorescent composition isover-printed by the well-known silk screen" process with an alcoholsolution of alcohol-modified urea-formaldehyde resin carrying adispersion of non-fluorescent irigredients or of ingredients fluorescinga color different from the color of the fluorescent surface to which thesolution is applied. The overprintedsoliition is then air-dried andbaked to fuse the urea-formaldehyde resin to the fluorescent surface.This manner of decorating a surface is particularly useful forname-plates and instrument panels which arelikely to be subjected towear or abrasion, since the resultant glassy surface is extremelyresistant to scratching.

Example B.--A sheet having a surface of our fluorescent composition isreverse-printed by lithography, for example, with a non-fluorescent inkto form a mask defining fluorescent digits. letters and/or symbols. Ifthe fluorescent surface is too rough to be printed accurately or withthe required degree of fineness, or, if the fluorescent surface is notreceptive to the non-fluorescent ink, the surface may be rendered smoothand ink receptive by coating the fluorescent surface prior to printingwith a suitable smooth, ink-receptive clear lacquer. The reverse printedsurface is then over-coated with a transparent lacquer.

preferably an alcohol solution of alcohol-modified urea-formaldehyderesin air-dried and fused upon the reverse-printed surface. In order tominimize glare, the transparent over-coating may be abraded to impartasatin flnish. This manner of decorating a fluorescent surface isparticularly useful when sharp, fine definition of digits, letters,and/or symbols is required.

Example C'.A transparent film, such as a film of vinyl copolymers, forexample, is printed in reverse with a non-fluorescent ink. The printedsurface of. the film is then laminated to an article having a surface ofour fluorescent composition, either by heat and pressure when the filmis thermo-adhesive or by means of a suitable transparent adhesive. Tominimize glare, the surface of the film may be abraded after lamination,or. in the case of thermo-plastic films, if the surface of the plate orroll which presses and laminates the film to the fluorescent surface hasa roughened or satin finish, such a finish will be imparted to thelaminated fllm. This manner of decorating is also particularly usefulwhen sharp definition of fluorescent characters is required.

Example D.-A sheet having a surface of our fluorescent composition isover-coated with a suitable clear non-yellowing lacquer and then coveredwith a suitable black or similar visible ably thermo-setting lacquers toprovide a tough wear and scratch resistant surface. The black coveringlacquer is then etched or engraved through to the clear over-coat toreveal the fluorescent surface. While this method does not afford thespeed of printing, as in the foregoing methods, it does permit theproduction of uniformly accurate engraved dials more rapidly and cheaplythan engraved dials known to the prior art. In the prior art, the mostaccurate luminescent dials were obtained by engraving black metal platesand then hand-filling the engraved plates with luminescent material,such as radium paint. Our method eliminates the tedious and non-1miformhand filling and the speed of; engraving through the relatively soft andthin lacquer is obviously greater than thespeed of engraving metal to agreater depth.

From the foregoing, it is apparent that this invention is not limited tothepartlcular application or manner of using it, but, in view of thisdisclosure, may be modified and varied by those skilled in the art fromthe preferred embodiments and applications we have disclosed. This invention, therefore, is not limited to the particular embodiment disclosed,either in whole or in part, but only by the following claims.

What is claimed is:

1. The method of making a fluorescent device for use at a distancefrom asource of fluorescigenous radiations, comprising impregnating a plasticmaterial, while in a plastic condition, with a fluorescent dye andadhering a backing of white non-fluorescent cellulose material to saidfluorescent material'so that when fluoresclgenous radiations aredirected upon said plastic material impregnated with fluorescent dye,the fluorescent energy within the plane of the plastic material isgreatly increased.

2. A fluorescent device for use at a distancefrom a source offluorescigenous radiations comprising a front member of plastic materialimpregnated with a fluorescent dye and a back member of non-fluorescentwhite cellulosematerial, the two members being adhered together to forma unitary structure so that, when fluorescigenous radiaitons aredirected upon said front member impregnated with a fluorescent dye, thefluorescent energy within the plane of the front member is greatlyincreased.

JOSEPH L. 'SWITZER.

ROBERT C. SWITZER.

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